1. Field of the Invention:
The present invention relates to novel fine powders of stabilized zirconia, to a process for the preparation thereof, and to the use of such powders for the production of ceramic materials having desirable mechanical, thermomechanical and electrical properties.
2. Description of the Prior Art:
Stabilized zirconia, and in particular zirconia stabilized with yttrium, magnesium, calcium or cerium values, is frequently used for the production of ceramic shaped articles.
It is known to this art that the production of dense, high purity ceramic materials having good homogeneity, relative both to chemical composition and to microstructure, is dependent on first providing special powders which are both very fine and highly homogeneous chemically. However, the preparation of such very fine powders presents various problems in relation to their processing parameters.
Among the several processes that currently exist for the preparation of such powders, one of the most interesting entails heat treating fine droplets obtained by the pulverization (or atomization) of a solution of precursors of the desired product.
Thus, in American Ceramic Society Bulletin, 65, No. 10, pp. 1399-1404 (1986), a process is described for the preparation of yttriated zirconia powder by the heat treatment of fine droplets consisting of a mixture of zirconium alkoxides and yttrium in solution in an organic solvent, (more precisely, a mixture of zirconium n-butoxide and yttrium isopropoxide in solution in anhydrous ethanol), with the fine dispersion of droplets being provided by means of an atomizer equipped with an ultrasonic generator.
However, such a process has several disadvantages, both relative to its application and to the powders obtained.
On the one hand, it requires alkoxy compounds; these compounds are expensive and are not readily available commercially.
On the other hand, it requires expensive and sometimes dangerous organic solvents, which are lost in the drying stage and which render the process particularly uneconomical.
Finally, the powders obtained by this process have capabilities in regard to forming and sintering which appear to be insufficient, especially concerning raw densities and final densities after sintering, which indicates an inadequate chemical and/or morphological quality of the powders themselves.